Nerve Growth Factor (NGF) is the prototypic and best studied member of the Neurotrophin family of neuronal growth factors, which are required for the survival and maintenance of many neuronal populations throughout the peripheral and central nervous systems. The principal mode of NGF signaling occurs over long distances, and has been postulated to occur by internalization and retrograde transport of an NGF-receptor complex within a "signaling endosome" from the nerve terminal to the cell body. The process by which the endosome is formed and trafficked, as it relates to intracellular signaling, has remained largely intractable due to a lack of understanding of the mechanism of internalization and tools with which to manipulate the endosome. We have discovered, through our recent identification of a protein we term "Pincher," the means to attack this important problem. Pincher mediates the formation of an endosome from which NGF mediates long-term signaling. Our preliminary findings suggest a model whereby signals emanating from the signaling endosome are fundamentally different from those generated at the plasma membrane, permitting differential signaling during and after retrograde transport to the cell body. To further explore and extend this model, we propose two specific aims: (1) to determine the relative importance of the differential signaling pathways mediated by NGF at the plasma membrane vs. the endosome and (2) to elucidate the process by which Pincher forms and trafficks signaling endosomes. Our proposed studies are intended to elucidate the mechanism by which Neurotrophins such as NGF regulate neuronal phenotype and survival. Neuronal death and defective phenotypic function are the major causes of nervous system disorders such as those seen in Parkinson's and Alzheimer's diseases, stroke, and peripheral neuropathies. Our work addresses these diseases of the nervous system, in which trophic support is defective and/or restoration of such support can be therapeutic in preventing neuronal loss and dysfunction. An understanding of the mechanisms for trophic factor signaling and delivery as proposed herein is essential to the rational design of therapeutics for combating these diseases.